This invention relates to dry pumps and in particular to the clearing of particulate dirt from dry pumps.
Dry pumps typically comprise non-contacting, self-valving mechanisms and no oil or lubricants in the pumping mechanism. The component parts of these pumps are manufactured to tight tolerances to provide fixed running clearances between components and reduce friction or other reactive forces, which may reduce the efficiency of the pump mechanism. The pumps are used in many manufacturing applications, one of the major of which is semi-conductor manufacture. The pumps are used to provide the very clean, near vacuum environment needed for the manufacture of quality semi-conductor products. The skilled addressee will no doubt be familiar with other common applications of dry pump technology.
Many industries including the semi-conductor industry produce particulate or powderous waste or bi-products which are withdrawn from the manufacturing environment by pumps such as the dry pumps to which this invention relates. In the semi-conductor industry it is usual for manufacturing lines to run twenty four hours a day, thus, dry pumps used in this application are in continuous use except where there is a need for a manufacturing line change or maintenance or repair of the pump. The pumps have an inlet purge function on shut down for evacuating contaminants from the pump mechanism, but these purge functions rarely operate one hundred percent efficiently and some level of particulate contamination invariably remains within the pump.
Running temperatures for dry pumps in semi-conductor manufacturing lines are typically around 120° C., when the pumps are switched off, they cool to normal room temperature (around 19° C.), the components (such as rotors and stators in the pump mechanism) contract, reducing the running clearances between them and any particulate contaminants present in the mechanism are compacted in between the contracted components. On restart, where the torque required to overcome the friction caused by the presence of these particulate materials compacted between the components is higher than the operational torque of the pump, start-up failure occurs.
The present invention aims to maintain running clearances of dry pumps and minimise the occurrence of restart failure due to compacted particulate contaminants.